Polyaddition products containing hydroxyl and uretdione groups, process for their preparation, their use for the production of highly reactive polyurethane powder coatings which are free from elimination products, and the polyurethane powder coatings produced accordingly

ABSTRACT

Polyaddition products containing hydroxyl and uretdione groups, a process for their preparation, their use for the production of highly reactive polyurethane (PUR) powder coatings which are free from elimination products and which crosslink to give light-stable and weather-stable coating films of high gloss, and the powder coatings produced accordingly are provided.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to polyaddition products containinghydroxyl and uretdione groups, a process for their preparation, theiruse for the production of highly reactive polyurethane (PUR) powdercoatings which are free from elimination products and which crosslink togive light-stable and weather-stable coating films of high gloss, andthe powder coatings produced thereby.

[0003] 2. Discussion of the Background

[0004] DE-C 30 30 572 presents a process for the preparation ofpolyaddition products which contain uretdione groups, and the productsprepared accordingly. These are reaction products of theisocyanurate-free uretdione (UD) of3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophoronediisocyanate, IPDI)—which can be prepared according to DE-C 30 30 513 orDE-C 37 39 549—with diols and, if desired, monoalcohols or monoamines.The reaction can be carried out in bulk or else in the presence ofappropriate solvents. However, so far, in practice, this class ofcrosslinking agent has been produced in economically significant,saleable quantities only in a suitable solvent under mild conditions, atabout 60° C., so as to avoid thermal ring cleavage during the synthesis.Preparation in bulk (i.e. in the absence of solvent) has not previouslygone beyond the laboratory scale, since the viscosity reachesunmanageable levels during the reaction as a function of the molecularmass of the crosslinking agent. While DE-C 3030572 indicates thatincreasing the reaction temperature can operate as a means ofcontrolling the reaction viscosity this measure is somewhat limitedsince higher temperatures can lead to detrimental effects on thereaction products.

[0005] This limit is also evident from the examples of DE-C 30 30 572which use a product having a molecular weight of not more than 3,000 orat a uretdione/diol molar ratio of 5:4 for a uretdione grade having afree NCO content of 17 and a total NCO content of 37.8% by weight. Ifthe free NCO content of the isophorone diisocyanate uretdione increasesfor a constant total NCO content (i.e. there is a simultaneous decreasein the degree of oligomerization and thus also in the molecular mass ofthe uretdione employed), then there is a corresponding decrease in themolecular mass of the uretdione group-containing polyaddition products.For the reasons given above, there seems little point in the preparationof uretdione group-containing polyaddition products of high molecularmass for use as crosslinking agents in the production of PUR powdercoatings. This is also reflected in DE-C 30 30 539 and DE-C 30 30 588.

[0006] In DE-C 30 30 539 the molecular weights claimed are between 550and 4,300, preferably between 1,500 and 2,000, and the uretdione/diolmolar ratios are between 2:1 and 6:5, preferably between 3:2 and 5:4.

[0007] In DE-C 30 30 588 the claimed molecular weights are very similar,namely from 500 to 4,000, preferably between 1,450 and 2,800 at auretdione/dial molar ratio comparable with that of DE-C 30 30 539.

[0008] Decisive disadvantages of the PUR powder coatings in accordancewith the teachings of DE-C 30 30 539 and DE-C 30 30 588, which are freefrom elimination products, include the limited possibilities forcombination with polymers containing hydroxyl groups. In DE-C 30 30 539,high functionalities of from ≧3.4 to ≦7, preferably from 3.7 to 4.5,were necessary. In order to achieve the high crosslinking densityrequired for high-quality PUR powder coatings, it was necessary tocompensate for the chain-terminating components of the crosslinkingagent. In DE-C 30 30 588, it was necessary to take account of the freeNCO content of the crosslinking agents in so far as the functionality ofthe hydroxyl group-containing polymers is to be adapted to the free NCOcontent in order to avoid gelling during extrusion, and therefore tosuppress losses in the quality of the coatings. It was necessary tolimit the OH functionality to from ≧2.2 to ≦3.5, preferably from 2.5 to3.4. Complex investigation was and still is necessary in order to tailorthe resin and curing agent to one another.

[0009] In DE-C 30 30 572, polyaddition products which contain uretdionegroups and terminal OH groups are described in one example and areclaimed. The scope corresponds to the polyaddition product specifiedabove. However, the OH-terminal polyaddition products have so faracquired no importance in the PUR powder coating sector, since there wasno economic value seen in comparing with the other crosslinking agents(see Example 5 of DE-C 30 30 572 in comparison with the remainingexamples). The numbers speak for themselves. These and chemical reasons,namely the uncontrolled polyaddition of the free OH groups with NCOgroups, which are additionally produced by uretdione cleavage duringsynthesis, have been considered as sufficient to attach no importance tothis kind of crosslinking agent.

SUMMARY OF THE PRESENT INVENTION

[0010] Accordingly, one object of the present invention is to providepolyaddition products which contain hydroxyl and uretdione groups, whichare useful as crosslinking agents for the production of PUR powdercoatings which are free from elimination products.

[0011] A further object of the present invention is to provide PURpowder coatings produced from polyaddition products containing bothhydroxyl and uretdione groups.

[0012] A further object of the present invention is to provide a methodsfor the production of polyaddition products which contain both hydroxyland uretdione groups, in which the methods can be either solvent free orsolution based methods.

[0013] These and other objects of the present invention have beensatisfied by the discovery or polyaddition products containing hydroxyland uretdione groups and having high molecular masses which are obtainedby reacting

[0014] I. from 40 to 85% by weight of the uretdione of isophoronediisocyanate and

[0015] II. from 60 to 15% by weight of diols and/or chain extenders,

[0016] wherein the polyaddition products have terminal hydroxyl groups,have a functionality of 2 and a molecular mass of between 4,500 and10,000, preferably between 5,500 and 7,000, which can be formulated, incombination with hydroxyl group-containing polymers, to give PUR powdercoatings which, possess heightened reactivity and lead to a gloss whichis outstanding for PUR powder coatings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention accordingly relates to polyadditionproducts which contain hydroxyl and uretdione groups and are producedfrom the uretdione of isophorone diisocyanate and diols and/or chainextenders.

[0018] The invention also relates to the use of the polyadditionproducts in transparent or pigmented PUR powder coatings of highreactivity and excellent gloss which are free from elimination productsand which are produced from the bifunctional polyaddition products, freeof blocking agents and containing hydroxyl and uretdione groups, andfrom hydroxyl group-containing polymers and the additives customary inPUR chemistry.

[0019] The isocyanurate-free uretdione of isophorone diisocyanate ishighly viscous at room temperature with a viscosity of greater than 10⁶mPa•s; at 60° C. the viscosity is 13·10³ mPa•s and at 80° C. it is1.4·10³ mPa•s. The free NCO content is between 16.8 and 18.5% by weight,indicating that high proportions of the polyuretdione of IPDI must bepresent in the reaction product. The monomer content is ≈1%. The totalNCO content of the reaction product after heating at 180−200° C. is37.5−37.8% by weight.

[0020] Diols which are suitable for the preparation of the polyadditionproducts according to the present invention, include those diolsconventionally used in PUR chemistry, with particular preference givento ethylene glycol (E), butane-1,4-diol (B), pentane-1,5-diol (P),hexane-1,6-diol (HD), 3-methylpentane-1,5-diol (Pm), 2,2,4(or2,4,4)-trimethylhexanediol (TMH-d) and neopentylglycol hydroxypivalate(Eg).

[0021] The polyaddition products of the present invention advantageouslycontain chain extenders in the form of linear polyesters which containhydroxyl groups and have a molecular mass between 250 and 2,000,preferably from 300 to 1,500. They are prepared by, for example,combination of diols and dicarboxylic acids.

[0022] To prepare the chain extenders—linear polyesters containinghydroxyl groups—it is preferred to employ not only the above-mentioneddiols but also 2-methylpropanediol, 2,2-dimethylpropanediol (NPG),diethylene glycol, dodecane-1,12-diol (C₁₂) and trans- andciscyclohexanedimethanol (CHDM).

[0023] The preferred dicarboxylic acids include aliphatic and optionallyalkyl-branched acids, such as succinic, adipic (As), suberic, azelaicand sebacic (Sb) acid, and 2,2,4 (or 2,4,4)-trimethyladipic acid. Alsoincluded are lactones and hydroxycarboxylic acids, such asε-caprolactone and hydroxycaproic acid.

[0024] The diol/chain extender mixtures used in the present inventionhave a diol/chain extender ratio of from 5:95 to 90:10. The products ofthe invention can be prepared either in solvent or in bulk (i.e. withoutsolvent).

[0025] The polyaddition products according to the invention can beobtained, inter alia, by a process such as the one described below.

[0026] The reaction in solvent is carried out at temperatures of from 50to 100° C., preferably between 60 and 90° C. The OH component, diolsand/or chain extenders, are added as initial charge and the uretdione isadded as rapidly as possible while preventing the reaction temperaturefrom exceeding the limit specified above. The reaction is complete afterfrom 30 to 150 minutes. Subsequently the solvent is removed. Apparatussuitable for this purpose include evaporation screws, filmtruders or,alternatively, spray-dryers.

[0027] Suitable solvents for the reaction include benzene, toluene orother aromatic or aliphatic hydrocarbons, acetates such as ethyl orbutyl acetate, ketones such as acetone, methyl ethyl ketone and methylisobutyl ketone, or chlorinated aromatic and aliphatic hydrocarbons, aswell as any desired mixtures of these or other solvents which are inertto the reaction conditions and non-reactive with the reactioncomponents.

[0028] The solvent-free and continuous preparation of the productsinvolves intensive kneading in a single- or multi-screw extruder, inparticular in a twin-screw extruder. The solvent-free synthesis requirestemperatures of significantly >120° C. to 190° C. It came as a surprisethat temperatures this high could be used for the uretdione syntheses.These temperatures are well within the range in which uretdionesunblock, meaning that high contents of free isocyanate can occur andproduce uncontrolled and undesired side reactions. This problem wasconsidered particularaly significant for the synthesis of uretdionepolyaddition products containing hydroxyl groups, and thus it was allthe more surprising that this synthesis could be carried out. Factorswhich proved advantageous in the solvent free synthesis were the shortreaction times of <5 minutes, preferably <3 minutes, more preferably <2minutes. A further principle is that the short exposure to heat issufficient to give a homogenous mixture of the reactants and to causethem to react completely or very substantially. Subsequently, controlledcooling is carried out in accordance with the development ofequilibrium, and, if necessary, the reaction is taken to completion.

[0029] The reaction products are supplied to the kneading apparatus inseparate product streams; it is possible to preheat the startingcomponents at up to 100° C., preferably up to 80° C. If there are morethan two product streams, then these can also be metered in batches.Diol, chain extender, catalysts, or other conventional coatingsadditives, such as levelling agents and/or stabilizers, or mixturesthereof can be combined into one product stream. The same applies tothose which are inert towards isocyanate groups: catalysts and,correspondingly, the above-mentioned coatings additives.

[0030] Similarly, the sequence of the product streams can be varied, andthe point of entry for the product streams may be at different locationsalong the length of the intensive kneading apparatus.

[0031] Known processes and technologies are used for the secondaryreaction, cooling, comminution and bag-filling.

[0032] In order to accelerate the reaction of polyaddition, it is alsopossible to use conventional PUR catalysts. These are employed in aconcentration of from 0.01 to 1% by weight, preferably from 0.03 to 0.5%by weight, based on the reaction components employed. Catalysts whichhave proven particularly suitable are tin(II) and tin(IV) compounds.Most preferred as catalyst is dibutyltin dilaurate (DBTL). However,other catalysts would not be regarded as unsuitable per se.

[0033] The present invention relates, furthermore, to the use of thepolyuretdione addition products according to the invention, containinghydroxyl and uretdione groups, in PUR powder coatings, which aresurprisingly distinguished by heightened reactivity. Entirelysurprisingly, therefore, the curing conditions can be reduced distinctlyin comparison with those previously known, which is significant both oneconomic and on ecological grounds.

[0034] The present invention further relates to polyurethane powdercoatings which are free from elimination products and which comprise thepolyaddition products according to the invention in combination withhydroxyl group-containing polymers.

[0035] Suitable co-reactants for PUR powder coatings are compounds whichcontain one or more functional groups which react with isocyanate groupsduring the curing process as a function of temperature and time, such ashydroxyl, carboxyl, mercapto, amino, urethane and (thio)urea groups.Polymers which can be employed include both condensation polymers andaddition polymers.

[0036] Preferred polymeric components include polyethers,polythioethers, polyacetals, polyesteramides, epoxy resins containinghydroxyl groups in the molecule, amino resins and their modificationproducts with polyfunctional alcohols, polyazomethines, polyurethanes,polysulphonamides, melamine derivatives, cellulose esters and ethers,partially hydrolysed homo- and copolymers of vinyl esters, polyestersand acrylate resins, with polyester and acrylate resins being mostpreferred.

[0037] Carboxylic acids which are preferred for the preparation of thepolyesters include aliphatic, cycloaliphatic, aromatic or heterocyclicacids or combinations thereof and may, if desired, be substituted by oneor more halogen atoms or unsaturated or both and their esters oranhydrides. Suitable carboxylic acids include succinic, adipic (AS),suberic, azelaic, Bebacic, phthalic, terephthalic (Ts), isophthalic(Is), trimellitic, pyromellitic, tetrahydrophthalic, hexahydrophthalic,hexahydroterephthalic, di- and tetrachloraphthalic,endomethylenetetrahydrophthalic, glutaric, maleic and fumaric acidsand—where accessible—their anhydrides, dimethyl terephthalate (DMT),bisglycol terephthalate and also cyclic monocarboxylic acids such asbenzoic acid, p-tert-butylbenzoic acid or hexahydrobenzoic acid.

[0038] Examples of suitable polyhydric alcohols include ethylene glycol,1,2-propylene glycol and 1,3-propylene glycol, 1,4-butylene glycol and2,3-butylene glycol, di-β-hydroxyethylbutanediol, hexane-1,6-diol,octane-1,8-diol, neopentylglycol, cyclohexanediol,1,4-bis(hydroxymethyl)-cyclohexane, 2,2-bis(4-hydroxycyclohexyl)propane,2,2-bis[4-(β-hydroxyethoxy)phenyl]propane, 2-methylpropane-1,3-diol,3-methylpentane-1,5-diol, 2,2,4(or 2,4,4)-trimethylhexane-1,6-diol,glycerol, trimethylolpropane, trimethylolethane, hexane-1,2,6-triol,butane-1,2,4-triol, tris(β-hydroxyethyl) isocyanurate, pentaerythritol,mannitol, sorbitol, diethylene glycol, triethylene glycol, tetraethyleneglycol, dipropylene xylylene glycol and neopentylglycol hydroxypivalate.

[0039] Mono- and polyesters of lactones, such as ε-caprolactone, orhydroxycarboxylic acids, such as hydroxypivalic acid, w-hydroxydecanoicacid, and ω-hydroxycaproic acid can also be employed. Also suitable arepolyesters of the above-mentioned polycarboxylic acids or their estersor anhydrides with polyphenols, such as hydroquinone, bisphenol A,4,4′-dihydroxybiphenyl or bis (4-hydroxyphenyl) sulphone; polyesters ofcarbonic acid obtainable from hydroquinone, diphenylolpropane,p-xylylene glycol, ethylene glycol, butanediol or hexane-1,6-diol andother polyols by conventional condensation reactions with carbonateproducing reagents such as phosgene or diethyl or diphenyl carbonate, orfrom cyclic carbonates such as glycol carbonate or vinylidene carbonate,by conventional polymerization procedures. Further compounds which canbe employed are polyesters of silicic acid, polyesters of phosphoricacid, such as those from methane-, ethane-, β-chloroethane-, benzene- orstyrenephosphoric acid, or the corresponding phosphoryl chlorides orphosphoric esters, and polyalcohols, or polyphenols of the typementioned above; polyesters of boric acid; polysiloxanes, such as theproducts obtained by hydrolysis of dialkyldichlorosilanes with waterfollowed by treatment with polyalcohols, and the products obtained byaddition reaction of polysiloxane dihydrides with functionalizedolefins, such as allyl alcohol or acrylic acid.

[0040] Other preferred polyesters include the reaction products ofpolycarboxylic acids with glycidyl compounds, as described, for example,in DE-A 24 10 513.

[0041] The hydroxyl group-containing polyesters which are preferred havean OH functionality of >2, an OH number of from 20 to 200 mg of KOH/g,preferably from 30 to 150 mg of KOH/g, a viscosity of <60,000 mPa•s,preferably <40,000 mPa•s at 140° C. and a melting point of ≧70° C. to≦120° C., preferably from 75° C. to 100° C.

[0042] Examples of glycidyl compounds which can be used are esters of2,3-epoxy-1-propanol with monobasic acids having from 4 to 18 carbonatoms (such as glycidyl palpitate, glycidyl laurate and glycidylstearate) or alkylene oxides having from 4 to 18 carbon atoms, such asglycidyl ether.

[0043] The dicarboxylic acids which can be used in this process includeall those polycarboxylic acids listed below under II; it is alsopossible to employ monocarboxylic acids, which are listed under III byway of example.

[0044] Other preferred components are monomeric esters, such asbis-hydroxy(alcohol) esters of dicarboxylic acids, esters ofmonocarboxylic acids with polyols having a functionality of more thantwo, and oligoesters which can be prepared by condensation reactionsfrom the raw materials which are customary in paint chemistry. Examplesof such customary materials include:

[0045] I. alcohols having 2 to 24, preferably 2 to 10, carbon atoms and2 to 6 OH groups which are attached to nonaromatic carbon atoms, such asethylene glycol, propylene glycol, diethylene glycol, dipropyleneglycol, butanediols, neopentyl glycol, hexanediols, hexanetriols,perhydrobisphenol, dimethylolcyclohexane, glycerol, trimethylolethane,trimethylolpropane, pentaerythritol, dipentaerythritol and mannitol;

[0046] II. di- and polycarboxylic acids having 4 to 36 carbon atoms and2 to 4 carboxyl groups and esterifiable derivatives thereof, such asanhydrides and esters, including phthalic acid (anhydride), isophthalicacid, terephthalic acid, alkyltetrahydrophthalic acid,endomethylenetetrahydrophthalic anhydride, adipic acid, succinic acid,maleic acid, fumaric acid, dimeric fatty acids, trimellitic acid,pyromellitic acid and azelaic acid;

[0047] III. monocarboxylic acids having 6 to 24 carbon atoms, such ascaprylic acid, 2-ethylhexanoic acid, benzoic acid, p-tert-butylbenzoicacid, hexahydro-benzoic acid, mixtures of monocarboxylic acids fromnatural oils and fats, such as coconut fatty acid, soya-oil fatty acid,castor oil fatty acid, hydrogenated and isomerized fatty acids, such as“Konjuvandol fatty acid and mixtures thereof; it is also possible to usefatty acid glycerides and to react them by transesterification and/ordehydration;

[0048] IV. monohydric alcohols having 1 to 18 carbon atoms, such asmethanol, ethanol, isopropanol, cyclohexanol, benzyl alcohol,isodecanol, nonanol, octanol and oleyl alcohol.

[0049] The polyesters can be obtained in a conventional manner bycondensation in an inert gas atmosphere at temperatures of from 100 to260° C., preferably from 130 to 220° C., in the melt or in an azeotropicprocedure, as described in, for example, Methoden der Organischen Chemie[Methods of Organic Chemistry] (Houben-Weyl), volume 14/2, 1-5, 21, 23,40, 44, Georg Thieme Verlag, Stuttgart, 1963 or in C. R. Martens, AlkydResins, 51-59, Reinhold Plastics Appl. Series, Reinhold PublishingComp., New York, 1961.

[0050] Preferred acrylate resins for possible use as OH components arehomo- or copolymers of monomers such as the following: esters of acrylicacid and methacrylic acid with dihydric, saturated, aliphatic alcoholshaving 2 to 4 carbon atoms, such as 2-hydroxyethyl acrylate,2hydroxypropyl acrylate, 4-hydroxybutyl acrylate and the correspondingmethacrylates; allyl acrylates and methacrylates having 1 to 18 carbonatoms in the alcohol component, such as methyl acrylate, ethyl acrylate,propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butylacrylate, 2-ethylhexyl acrylate, stearyl acrylate and the correspondingmethacrylates; cyclohexyl acrylate and methacrylate; acrylonitrile andmethacrylo-nitrile, acrylamide and methacrylamide; andN-methoxy-methyl(meth)acrylamide.

[0051] Particularly preferred acrylate resins are copolymers of

[0052] a. from 0 to 50% by weight of esters of acrylic or methacrylicacid with dihydric or polyhydric alcohols, such as 1,4-butanediolmonoacrylate, hydroxypropyl (meth)acrylate; and also vinylglycol,vinylthioethanol, allyl alcohol and 1,4-butanediol monovinyl ether;

[0053] b. from 5 to 95% by weight of esters of acrylic acid ormethacrylic acid with monohydric alcohols containing from 1 to 12 carbonatoms, such as methyl methacrylate, ethyl acrylate, n-butyl acrylate or2ethylhexyl acrylate;

[0054] c. from 0 to 50% by weight of aromatic vinyl compounds, such asstyrene, methylstyrene or vinyltoluene;

[0055] d. from 0 to 20% by weight of other monomers having functionalgroups, includes acrylic acid, methacrylic acid, crotonic acid, itaconicacid, maleic acid, fumaric acid, maleic anhydride, maleic monoesters,acrylamide, methacrylamide, acrylonitrile or N-methylol(meth)acrylamideand glycidyl(meth)acrylate, provided that the total of components a) andb) must be at least 5% by weight.

[0056] The acrylate resins can be prepared by conventionalpolymerization including bulk, solution, suspension, emulsion orprecipitation polymerization, but preferably by bulk polymerizationwhich, in turn, can be initiated by UV light.

[0057] Further polymerization initiators which are used are theconventional peroxides or azo compounds, such as dibenzoyl peroxide,tert-butyl perbenzoate or azobisiso-butyronitrile. The molecular weightcan be regulated using, conventional molecular weight regulator,including the sulphur compounds such as tertdodecanethiol.

[0058] Preferred polyethers can be prepared by the polyaddition of anepoxide, such as ethylene oxide, propylene oxide, butylene oxide,trimethylene oxide, 3,3-bis(chloromethyl) oxacyclobutane,tetrahydrofuran, styrene oxide, the bis(2,5-epoxypropyl) ether ofdiphenylolpropane or epichlorohydrin with itself, for example in thepresence of BF₃, or by the addition of the epoxide, if desired alone oras a mixture or in succession, with starting components containingreactive hydrogen atoms, such as alcohols or amines, including water,ethylene glycol, 1,3-propylene glycol or 1,2-propylene glycol,pentamethylene glycol, hexanediol, decamethylene glycol,trimethylolpropane, 4,41-dihydroxydiphenylpropane, aniline, ammonia,ethanolanine, ethylenediamine, di(βhydroxypropyl)methylamine,di(β-hydroxyethyl)aniline, hydrazine, and also hydroxyalkylated phenols,such as di(β-hydroxyethoxy) resorcinol.

[0059] It is also possible to employ polyureas and/or polyurethanescontaining hydroxyl groups in the process of the present invention.

[0060] As polyhydroxy compounds it is also possible, of course, toemploy mixtures of two or more polyhydroxy compounds as described above.

[0061] The ratio in which the hydroxyl group-containing polymers and theisocyanate component are mixed is selected such that 0.5-1.2, preferably0.8-1.1, most preferably 1.0, free and/or blocked NCO groups are presentper OH group.

[0062] For the production of PUR powder coatings, the isocyanatecomponent is mixed and homogenized in the melt with the appropriatehydroxyl group-containing polymer and, if desired, catalysts, pigments,fillers, levelling agents, such as silicone oil, and acrylate resins.This can be carried out in any suitable apparatus, such as a heatablekneading apparatus, but preferably by extrusion, in which case uppertemperature limits of from 130 to 140° C. should not be exceeded. Afterthe extruded composition has been cooled to room temperature andcomminuted appropriately, it is ground to give the ready-to-spraypowder. The application of the ready-to-spray powder to suitablesubstrates can be carried out by conventional processes, including, butnot limited to, electrostatic powder spraying, fluidized-bed sintering,or electrostatic fluidized-bed sintering. After the application of thepowder, the coated work-pieces are heated for curing purposes for from60 to 4 minutes at a temperature of from 150 to 220° C., preferably for30 to 6 minutes at from 160 to 200° C.

[0063] Having generally described this invention, a furtherunderstanding can be obtained by reference to certain specific exampleswhich are provided herein for purposes of illustration only and are notintended to be limiting unless otherwise specified.

EXAMPLES

[0064] A. Preparation of the polyaddition products according to thepresent invention, containing hydroxyl and uretdione groups

[0065] A1: Polyol chain extenders

[0066] General preparation procedure

[0067] The starting components—see Table 1—were placed in a reactor andheated to ≈140° C. using an oil bath. After the substances had verylargely melted, 0.1% by weight of di n-butyltin oxide was added ascatalyst. Elimination of water began at 150 to 160° C. Over the courseof 2 to 3 hours the temperature was raised to 180° C. to 190° C. and theesterification was brought to an end over a further 8 to 10 hours.Throughout the reaction period the bottom product was stirred and agentle stream of nitrogen was passed through the reaction mixture. Theacid number of the polyesters was in each case <2 mg of KOH/g. TABLE 1Polyol chain extenders Exam- Characteristics ple Starting components inmole OH number Viscosity 25° C. A1 As Sb NPG P HD mg KOH/g mPa · s 1 1 2335 ± 15 ≈1,500 2 1.25 2.25 290 ± 10 ≈1,950 3 1 2 335 ± 15 ≈1,270 4 1 2289 ± 10 ≈1,150 5 4 3 2 106 ± 7  ≈3,500 6 Polycaprolactones 216 Meltingrange from Interox-Capa 200 18-23° C. 7 Polycaprolactones 112 Meltingrange from Interox-Capa 210 112 30-40° C.

[0068] A2: Polyaddition products containing hydroxyl and uretdionegroups

[0069] General preparation procedures

[0070] A 2.1 from solvent

[0071] The polyol component—see Table 2—and the catalyst (0.03-0.5% byweight of DBTL), in solution in a solvent, were placed in the reactor.With vigorous stirring and under an inert gas atmosphere, the calculatedquantity of IPDI uretdione, in solution in the solvent, was added at arate such that the reaction temperature did not exceed 100° C. Thereaction was monitored by means of titrimetric determination of NCO andwas complete after 1 to 3 hours. The solvent was then removed, and theproduct was cooled and comminuted if appropriate.

[0072] A 2.2 without solvent

[0073] The IPDI uretdione at a temperature of 60 to 110° C. was fed intothe intake housing of a twinscrew extruder, the polyol component—seeTable 2—being metered in simultaneously at a temperature of 25 to 110°C. If desired, the uretdione and/or the polyol component contained thequantity of catalyst required—from 0.03 to 0.5% by weight of DBTL—basedon the end product.

[0074] The extruder employed was composed of ten housings of which fivewere heating zones. The temperatures of the heating zones were subjectto a wide range—between 50 and 180° C.—and could be controlledindividually. All of the temperatures were setpoint temperatures, withregulation in the housings being carried out by electrical heating andpneumatic cooling. The die element was heated by means of an oilthermostat. The speed of the two screws, fitted with conveying elements,was between 50 and 380 rpm.

[0075] The reaction product, obtained in quantities of from 10 to 130kg/h, was either cooled and then comminuted or shaped and bagged, or theactual melt was shaped, and the shaped articles were then cooled andbagged.

[0076] The physical and chemical characteristics of the process productsof the invention and the molar compositions are summarized in Table 2.TABLE 2 Composition (mole) Chemical and physical characteristics ChainNCO content Melting Glass Example IPDI extender (% by weight) rangetransition A 2 uretdione Diol (s) A1 free total ° C. temperature 1 (7)Eg (8) — 0 12.1 108-115 62-81 2 (7) Eg (3), C₁₂ (3), E (2) — <0.1 12.8110-113 65-87 3 (7) Eg (4), B (4) — <0.1 13.1 117-122 82-95 4 (7) Eg(4), TMH-d (4) — <0.1 12.5 101-103 56-72 5 (7) Eg (6), Pm (2) — 0 12.4108-111 61-78 6 (8) Eg (4), Pm (3), B (2) — 0.1 13.1 106-114 58-75 7 (8)TMH-d (6), B (3) — 0.1 13.6 111-115 63-81 8 (9) TMH-d (5), Pm (4), —<0.1 13.8 113-118 66-84 B (1) 9 (9) Eg (4), TMH-d (3) — 0.1 13.5 115-11968-87 B (2), E (1) 10 (7) B (4), E (2) 6 (2) <0.1 12.7 90-94 52-77 11(7) Eg (3.5), E (2.5) 6 (0.75) <0.1 12.8 110-113 65-87 TMH-d (1.25) 12(7) Pm (6.5) 6 (1.5) 0 11.0 83-89 44-60 13 (7) Eg (3.5), E (1) 7 (1)<0.1 10.1 81-86 41-57 TMH-d (2.5) 14 (7) Eg (3.5), HD (2) 6 (0.5) 0 11.591-94 45-60 E (1.5) 7 (0.5) 15 (7) Eg (3.5), E (3.5) 5 (0.5) 0 11.7 99-102 56-79 6 (0.5) 16 (6.5) Eg (3), P (2) E (1.5) 5 (0.5) 0 11.9101-108 65-86 6 (0.5) 17 (8) Eg (4), TMH-d (1.25) 5 (0.5) 0.1 12.2112-118 77-91 Pm (2), E (1) 6 (0.25)

[0077] TABLE 3 Composition (mole) Chemical and physical characteristicsChain NCO content Melting Glass Example IPDI extender (% by weight)range transition A 2 uretdione Diol(s) A 1 free total ° C. temperature 1(6) B (1) 1 (6) <0.1 9.9 85-92 61-66 2 (7) E (2) 1 (6) <0.1 10.8 88-9153-67 3 (7) E (4) 1 (4) 0 12.4 104-107 69-87 4 (7) B (4.75) 1 (3.25) 012.2 102-104 70-85 5 (7) TMH-d (7) 1 (1) <0.1 12.2 106-109 72-82 6  (7.5) P (6.75) 1 (1.75) 0 13.1 104-111 72-91 7 (8) Pm (7.75) 1 (1.25)0 13.4 111-117 81-96 8 (7) Pm (6.5) 2 (1.5) <0.1 12.3 112-115 75-90 9  (7.5) E (6) 2 (2.5) 0 12.7 110-118 77-95 10   (7.5) TMH-d (3) 2 (2.5)<0.1 12.3 108-115 71-86 E (3) 11 (7) TMD-d (6.5) 3 (1.5) <0.1 11.9 99-103 71-84 12 (8) HD (6.5) 3 (2) <0.1 12.6 105-114 74-87 13 (7) TMH-d(7) 4 (1) 0 12.2  99-102 74-90 14   (7.5) B (5.5) 4 (3) 0 12.3 112-11779-89 15 (8) Pm (7) 4 (2) <0.1 12.6 109-117 75-92 16 (7) Eg (3.25) 5(1.5) 0 9.8 73-77 41-55 Pm (3.25) 17 (7) TMH-d (3.75) 5 (0.75) 0 10.290-93 53-76 Eg (3.5) 18 (7) Eg (5) 5 (0.5) <0.1 11.9 107-110 67-88 E(2.5)

[0078] The IPDI uretdione produced by the known process had thefollowing NCO characteristics:

[0079] free: from 16.8 to 18.5% by weight

[0080] total: from 37.5 to 37.8% by weight

[0081] B Polyester

[0082] Table 4 below gives an overview of the polyesters on the marketwhich are employed for the formulation of PUR powder coatings. TABLE 4Chemical and physical characteristics Glass Name OH Acid Meltingtransition Viscosity Example Manufacturer of number number rangetemperature at 160° C. B country product mg KOH/g mg KOH/g ° C. ° C. mPa· s 1 Hoechst AG Alftalat 55-60 2-4 82-90 <50 24-29,000 Italy AN 739 2DSM Uralac 38-41   4-4.5 70-75   50 40,000 Netherlands P 1460 3 UCBCrylcoat 26-31 3-4 74-80 <50 33-38,000 Belgium 240

[0083] C Polyurethane powder coatings

[0084] General preparation procedure

[0085] The comminuted products, crosslinking agents, polyesters,levelling agent masterbatch and, if desired, catalyst masterbatch wereintimately mixed, together with the white pigment (if desired), in anedge runner mill and then homogenized in an extruder at not more than130° C. The extrudate was then cooled, fractionated and ground in a pinmill to a particle size <100 μm. The powder thus prepared was appliedusing an electrostatic powder spraying unit at 60 kV to degreased and—ifappropriate—pretreated iron panels which were baked in a circulating-airdrying cabinet at temperatures of between 160 and 200° C.

[0086] Levelling agent masterbatch

[0087] 10 percent by weight of the levelling agent—a commerciallyavailable copolymer of butyl acrylate and 2-ethylhexyl acrylate—werehomogenized in the melt in the corresponding polyester and, aftersolidifying, were comminuted.

[0088] Catalyst masterbatch

[0089] 5 percent by weight of the catalyst—DBTL—were homogenized in themelt in the corresponding polyester and, after solidifying, werecomminuted.

[0090] The abbreviations in the following tables denote: LT = layerthickness in μm KH = Koenig hardness (sec) (DIN 53 157) BH = Buchholzhardness (DIN 53 153) EI = Erichsen indentation (DIN 53 156) CH =crosshatch test (DIN 53 151) GG 60° ≮ = gloss measurement according toGardner (ASTM-D 523) Imp. rev. = impact reverse in g · m

[0091] TABLE 5 Pigmented powder coatings Example C Formulation 1 2 3 4 56 7 8 9 10 11 12 Crosslinking agent 25.98 20.84 14.5 26.44 21.36 24.8313.76 24.97 26.13 20.97 14.6 27.07 acc. to A 2 (2) (2) (2) (4) (5) (7)(7) (9) (10) (10) (10) (11) Table 2 (Example) Polyester acc. to 74.02 —— 73.56 — 75.17 — 75.03 73.87 — — 72.93 B 1 — 79.16 — — 78.64 — — — —79.03 — — Polyester acc. to — — 85.5 — — — 86.24 — — — 85.4 — B 2Polyester acc. to B 3 Notes: All formulations contain 40% by weight ofTiO₂ (white pigment) and each contain 0.5% by weight of levelling agentand benzoin and 0.15% by weight of DBTL; the OH/NCO ratio = 1:1 Coatingsdata LT 55-70 70- 55-80 60-75 65-80 55-70 60- 55-70 65- 60- 65-85 70-95KH 192 95 193 194 191 197 85 192 85 70 186 186 BH 100 200 100 111 100100 195 100 188 184 111 111 CH 0 111 0 0 0 0 111 0 100 100 0 0 GG 60° ≮88-89 0 92- 89- 90-91 88-90 0 88-89 0 0 92-93 89-92 EI >10 89- 93 919.5- 9.7- 90- 9.2- 90 90- >10 10 Impr. rev. > 92 >10 >10 9.8 10 9310 >10 91 >944.6 >944.6 944.6 >10 > > 806.4 806.4 >10 >944.6 > >10 >944.6 944.6 > 944.6 > 944.6 944.6 944.6 Notes: Curing conditions: 200°C./8 minutes or 180° C./15 minutes

[0092] TABLE 6 Pigmented powder coatings Example C 14 16 Formulation13 * 15 * 17 18 19 20 21 22 23 24 Crosslinking agent 29 24.62 16.4813.64 28.09 27.74 22.36 15.65 27.4 — — — acc. to A 2 (12) (12) (12) (12)(14) (15) (15) (15) (17) Table 2 (Example) Crosslinking agent — — — — —— — — — 31.21 29.38 16.74 acc. to A 2 (1) (2) (2) Table 3 (ExamplePolyester acc. to 71 75.38 — — 71.91 72.26 — — 72.6 68.79 70.62 — B 1 —— — — — — 77.64 — — — — — Polyester acc. to — — 83.52 86.36 — — — 84.35— — — 83.26 B 2 Polyester acc. to B 3 Notes: All formulations contain40% by weight of TiO₂ (white pigment) and each contain 0.5% by weight oflevelling agent and benzoin and 0.15% by weight of DBTL; the OH/NCOratio = 1:1, *OH/NCO = 1:0.8 Coatings data LT 70-75 80- 70- 65- 70-8550-65 65- 60-75 70- 60- 65-80 70-75 KH 188 95 90 85 183 182 80 185 85 75180 187 BH 118 186 185 183 111 100 184 100 181 182 105 100 CH 0 100 100111 0 0 100 0 100 100 0 0 GG 60° ≮ 89 0 0 0 89-90 88 0 92 0 0 88 91-92EI >10 90- 92- 93 >10 >10 89 9.3 89 89 >10 >10 Impr. rev. > 91 93 >10691.2 576 >10 576 9.9 >10 >944.6 >944.6 944.6 >10 >10 > 806.4691.2 > > > 944.6 944.6 944.6 806.4 Notes: Curing conditions: 200° C./8minutes or 180° C./15 minutes

[0093] TABLE 7 Pigmented powder coatings Example C 26 28 Formulation25 * 27 * 29 30 31 32 33 34 35 36 Crosslinking agent 26.59 14.9 25.5825.53 25.53 21.53 20.46 14.22 21.5 26.01 17.55 22.06 acc. to A 2 (3) (3)(4) (6) (6) (6) (6) (6) (8) (13) (17) (18) Table 3 (Example) Polyesteracc. to 73.41 — — 74.47 74.47 78.47 — — — 73.99 — — B 1 — — 74.42 — — —79.54 — 78.5 — — 77.94 Polyester acc. to — 85.1 — — — — — 85.78 — —82.45 — B 2 Polyester acc. to B 3 Notes: All formulations contain 40% byweight of TiO₂ (white pigment) and each contain 0.5% by weight oflevelling agent and benzoin and 0.15% by weight of DBTL; the OH/NCOratio = 1:1, *OH/NCO = 1:0.8 Coatings data LT 75- 75- 65- 60- 65-7550-55 55- 70-75 60- 50- 50-65 60 KH 90 85 80 75 184 182 75 185 80 70 186184 BH 185 188 184 184 100 111 184 100 183 185 100 100 CH 105 100 100100 0 0 100 0 100 100 0 0 GG 60° ≮ 0 0 0 0 89 90 0 91-92 0 0 90-91 89-90EI 88- 90- 89 88- 9.1-10 >10 89- >10 89- 88- >10 9.4- Impr. rev. 8991 >10 89 691.2 >944.6 90 >944.6 90 89 >944.6 10 >10 >10944.6 >10 >10 >10 >10 806.4 > > > > > > 806.4 691.2 944.6 944.6 944.6944.6 Notes: Curing conditions: 200° C./8 minutes or 180° C./15 minutes

[0094] TABLE 6 Pigmented powder coatings Example C 14 16 Formulation13 * 15 * 17 18 19 20 21 22 23 24 Crosslinking agent 29 24.62 16.4813.64 28.09 27.74 22.36 15.65 27.4 — — acc. to A 2 (12) (12) (12) (14)(15) (15) (15) (15) (17) Table 2 (Example) Crosslinking agent — — — — —— — — — 31.21 29.38 16.74 acc. to A 2 (1) (2) (2) Table 3 (ExamplePolyester acc. to 71 75.38 — — 71.91 72.26 — — 72.6 68.79 70.62 — B 1 —— — — — — 77.64 — — — — — Polyester acc. to — — 83.52 86.36 — — — 84.35— — — 83.26 B 2 Polyester acc. to B 3 Notes All formulations contain 40%by weight of TiO₂ (white pigment) and each contain 0.5% by weight oflevelling agent and benzoin 0.15% by weight of DBTL; the OH/NCO ratio =1:1, *OH/NCO = 1:0.8 Coatings data LT 70-75 80- 70- 65- 70-85 50-65 65-60-75 70- 60- 65-80 70-75 KH 188 95 90 85 183 182 80 185 85 75 180 187BH 118 186 185 183 111 100 184 100 181 182 105 100 CH 0 100 100 111 0 0100 0 100 100 0 0 GG 60° ≮ 89 0 0 0 89-90 88 0 92 0 0 88 91-92 ET >1090- 92- 93 >10 >10 89 9.3 89 89 >10 >10 Impr. rev. > 91 93 >10 691.2576 >10 576 9.9 >10 >944.6 >944.6 944.6 >10 >10 > 806.4 691.2 > > 944.6944.6 944.6 806.4 Notes: Curing conditions: 200° C./8 minutes or 180°C./15 minutes

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A polyaddition products containing hydroxyl anduretdione groups obtained by reacting I. from 40 to 85% by weight of anuretdione of isophorone diisocyanate and II. from 60 to 15% by weight ofone or more diols, one or more chain extenders or both, wherein thepolyaddition product has one or more terminal hydroxyl groups, afunctionality of 2 and a molecular mass of from 4,500 to 10,000.
 2. Thepolyaddition product of claim 1, wherein said molecular mass is from4,500 to 7,000.
 3. The polyaddition product according to claim 1,wherein said one or more diols are selected from the group consisting ofethylene glycol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol,3-methylpentane-1,5-diol, 2,2,4(2,4,4)-trimethylhexanediol (isomermixture) and neopentylglycol hydroxypivalate.
 4. The polyadditionproduct according to claim 1, wherein said one or more chain extendersare selected from the group consisting of linear polyesters containinghydroxyl groups having a molecular mass of from 250 to 2,000.
 5. Thepolyaddition product according to claim 4, wherein said linearpolyesters containing hydroxyl groups have a molecular mass of from 300to 1,500.
 6. The polyaddition product according to claim 4, wherein saidlinear polyesters containing hydroxyl groups are composed of at leastone diol monomer selected from the group consisting of ethylene glycol,butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol,3-methylpentanel,5-diol, 2,2,4(2,4,4)-trimethylhexanediol andneopentylglycol hydroxypivalate, 2-methylpropanediol,2,2-dimethylpropanediol, di-ethylene glycol, dodecane-1,12-diol, trans-and cis-cyclohexanedimethanol and at least one monomer selected from thegroup consisting of succinic, adipic, suberic, azelaic, sebacic, and2,2,4(2,4,4)-trimethyladipic acids (isomer mixture), ε-caprolactone andhydroxycaproic acid.
 7. The polyaddition product according to claim 1,wherein both diols and chain extenders are used in a diol/chain extenderratio of from 5:95 to 90:10.
 8. The polyaddition product according toclaim 1, wherein said reacting step is carried out in solvent, which isremoved after reaction has taken place.
 9. The polyaddition productaccording to claim 1, wherein said reacting step is carried out withoutsolvent in an intensive kneading apparatus.
 10. The polyaddition productaccording to claim 9, wherein said intensive kneading apparatus is atwin-screw extruder.
 11. The polyaddition products according to claim 1,wherein said reacting step requires the presence of a catalyst in aconcentration of from 0.01 to 1% by weight, based on the startingmaterials.
 12. The polyaddition product according to claim 11, whereinsaid catalyst is an organotin catalyst.
 13. The polyaddition productaccording to claim 12, wherein said organotin catalyst is dibutyltindilaurate.
 14. The polyaddition product according to claim 11, whereinsaid catalyst is used in a concentratio of from 0.03 to 0.5% by weight,based on the starting materials.
 15. A process for the preparation ofpolyaddition products containing hydroxyl and uretdione groups, from theuretdione of isophorone diisocyanate and from diols, chain extenders ora mixture thereof, comprising: reacting: I. from 40 to 85% by weight ofthe uretdione of isophorone diisocyanate and II. from 60 to 15% byweight of one or more diols, one or more chain extenders or both,wherein said reacting step is carried out (1) at temperatures of from 50to 100° C. in a solvent which is removed after reaction has taken place,or (2) without solvent in an intensive kneading apparatus attemperatures of from 120 to 190° C., optionally with the use of from0.01 to 1% by weight of catalyst, based on the starting materials. 16.The process of claim 15, wherein said intensive kneading apparatus is atwin-screw extruder.
 17. The process according to claim 15, wherein saidone or more chain extenders are selected from the group consisting oflinear polyesters containing hydroxyl groups and having a molecular massbetween 250 and 2,000.
 18. A polyurethane powder coating which is highlyreactive and free from elimination products comprising one or morepolyaddition products as claimed in claim 1 and one or more polymerscontaining hydroxyl groups.
 19. The polyurethane powder coatingaccording to claim 18, wherein said coating has an OH/NCO ratio of from1:0.5 to 1:2.
 20. The polyurethane powder coating according to claim 19,wherein said OH/NCO ratio is from 1:0.8 to 1:1.
 21. The polyurethanepowder coating according to claim 20, wherein said OH/NCO ratio is 1:1.22. The polyurethane powder coating according to claim 18, furthercomprising one or more catalysts at a total catalyst concentration offrom 0.03 to 0.5% by weight.
 23. The polyruethane powder coatingaccording to claim 22, wherein said total catalyst concentration is from0.05 to 0.15% by weight.
 24. The polyurethane powder coating accordingto claim 18, wherein said one or more polymers containing hydroxylgroups are polyesters having a functionality>2, an OH number of from 20to 200 mg of KOH/g, a viscosity<60 000 mPa•s at 160° C., and a meltingpoint≧70° C. and ≦120° C.
 16. A coated substrate comprising apolyurethane powder coating according to claim 18 and a substrate.